A temporal rift opens, and the USS Enterprise-C emerges, changing the timeline into a reality where the Federation is in a bitter war with the Klingon Empire. The only person on the USS Enterprise-D who realizes that something is not right is Guinan, and she must help return the displaced starship to its proper time, in order for the Enterprise-D crew to save themselves.

Contents

Worf is sitting alone in Ten Forward when Guinan comes to his table and hands him a glass and asks him to try the drink. Worf tries it and is extremely surprised to find that he loves the drink. Guinan tells Worf it's an Earth drink, prune juice, which Worf refers to as "a warrior's drink." Guinan notes that Worf always drinks alone and suggests that he seek out some companionship. However Worf says he would need a Klingon woman for companionship as Earth females are too fragile. He then laughs loudly when Guinan tells him there are women aboard who might find him tame, a thought he considers impossible. When Guinan playfully calls him a coward for saying he'll never know when she says he should find out, Worf says he was merely concerned for the safety of his fellow crewmates. Just then, a strange phenomenon appears outside Ten Forward's windows and Worf is called to the bridge. Guinan stands up and looks toward the phenomenon and simply utters "No."

Arriving on the bridge, Worf is told that the USS Enterprise-D has encountered what appears to be a strange temporal rift in space. Investigating, the crew are unable to confirm exactly what and precisely where the phenomenon is.

Worf reports a change in sensor readings. CaptainPicard turns back on Worf and asks Data, who begins to check the sensors. As a starship emerges from the rift, the bridge of the Enterprise changes. It now appears much darker and the crew's uniforms have more of a militaristic flair to them. No one present seems aware of the changes. Picard turns to the tactical station and asks if the ship that emerged is an enemy vessel. However Worf is gone, and the late Natasha Yar stands in his place. Troi has also disappeared.

Down in a much more brightly lit Ten Forward, as Guinan clears a table, everyone is in uniform and all are armed. She straightens up and senses something isn't right, that everything has changed.

As the starship clears the rift, Tasha confirms it as a Federationstarship and tries to access the ship's registry. CommanderRiker notes the crew must have had a rough ride. Yar reads the ship's registry as NCC-1701-C, which causes Picard and Riker to turn toward her in astonishment as Yar finishes reading the name of the ship... USS Enterprise.

"Military log, combat date 43625.2. While investigating an unusual radiation anomaly, the Enterprise has encountered what could almost be called a ghost from its own past - the Enterprise-C, the immediate predecessor to this battleship."

On the altered bridge of the Enterprise, Data reports that the sensors confirm that the other ship's hull and engine components are of the Enterprise-C's time period. When Wesley Crusher mentions that the Enterprise-C was destroyed with all hands more than twenty years previous, Data corrects him, saying that the ship was presumed destroyed near Narendra III, a Klingon outpost. Captain Picard wonders if the ship was adrift for all the years it's been missing or perhaps traveled through time. Data says that if time travel does turn out to be the proper theory then the phenomenon they have encountered is a temporal rift, such as a Kerr loop in space which is most certainly unstable and capable of collapsing at any time. Yar then reports that she is able to scan the interior of the ship and she reports heavy damage but she does detect sporadic life signs. Riker calls sickbay to prepare emergency teams and orders the transporter rooms to standby, but Picard belays Riker's orders, reminding him that if the other ship has indeed traveled through time then they could be dealing with variables that might alter the flow of their history. At that moment, Tasha tells Picard that Enterprise-C is sending out an audio distress call and Picard orders it put on speakers.

"This is Captain Garrett of the starship Enterprise to any Federation ship. We have been attacked by Romulan warships and require immediate assistance. We've lost warp drive, life support is failing."

Riker mentions that there was no record of Romulans ever attacking Enterprise-C and then Yar reports the voice message has terminated and they are only receiving an automated signal from the vessel. Picard then orders a channel opened and tells the Enterprise-C that he is "Captain Picard of the Federation... of a Federation starship" and tells Garrett to stand by for emergency teams. He then tells Riker to assess the situation and attend to their wounded and above all, avoid all discussions of where and when they are. Riker says he will and takes Yar with him for the away team. Just then, Crusher tells Picard that Starfleet monitor stations are detecting Klingon ships in the area and on their way, and Picard orders battle alert, condition yellow.

Meanwhile, the Enterprise-C is in bad shape. The away team beams aboard the bridge and Dr. Beverly Crusher reports the majority of the bridge crew are dead and that the captain is seriously injured. She and Riker tell Garrett they are from a Federation ship and that they are here to assist. When Dr. Crusher tells Riker she must take Garrett back to Enterprise, Garrett demands an explanation but Riker simply tells her they are from a Federation ship that answered their distress signal and that they will answer all questions but for now they must get her to sickbay. With that, Garrett relents and allows Crusher to transport themselves back directly to sickbay.

At the same time, chief engineerGeordi La Forge tells Riker the ship is in pretty bad shape. Riker tells him if they can't stabilize life support they will have to evacuate the ship, but La Forge says he can do it but he'll have to go to engineering and calls a damage control party to engineering. Then Yar and Riker notice some rustling underneath some debris. They pull the debris off and discover another survivor, Lt.Richard Castillo, the ship's helmsman.

Picard arrives back on the bridge in time for a report from the away team. Riker reports back that they've stabilized life support and that La Forge is working on repairing the main power couplings. He also tells Picard that there are 125 survivors aboard the Enterprise-C. When Picard asks for recommendations, Riker says that he'd hate to have to lose the ship as Starfleet could certainly use another vessel, even if it is old. While Picard agrees, he also cautions Riker that they can't stay in the area too long. Picard allows Riker nine hours to get the Enterprise-C under-way to Starbase 105. If they are unable to do so, then the survivors will be evacuated and the ship will be destroyed.

At that moment, Guinan enters the bridge. Seemingly disoriented, she walks up to Picard. When Picard notices her she says she needs to speak to Picard, claiming that things are "not the way they're supposed to be."

In his ready room, Picard questions Guinan's "discovery." Things don't feel "right" to her, things like the bridge, the crew's uniforms, their attitudes. Picard asks what has changed and he counters that this is the way it has always been, and asks what else has changed. Families, Guinan says. There should be children on the Enterprise. Astounded, Picard scoffs at the idea – the Federation is at war. No, Guinan says. The Federation is not at war, or at least it's not supposed to be. She tells Picard that Enterprise isn't a ship of war, but of peace. And the only way to restore that truth... is to send the Enterprise-C back to its own time as it does not belong in the present.

Reeling from this revelation, Picard arrives in sickbay to meet Captain Garrett, who has just undergone surgery. Garrett asks where they came from, but Picard deflects it with wanting to know how her ship ended up here. Garrett tells Picard that they were responding to a distress signal from the Klingon outpost on Narendra III and asks if Picard heard it, but he says they didn't. Garrett says she's never seen a sickbay like the one she's in, not even on a starbase. Nor has she ever seen their uniforms. She asks what ship she's on. Beverly urges Garrett to be still and relax. but she insists on finding out what ship she is on. Picard tells her that she is aboard the Enterprise, 1701-D, a revelation that stuns Garrett. Picard tells her they have traveled 22 years into the future. Garrett wants to know if the crew has been informed and Picard says they haven't. Garrett says she should inform them and Picard offers to but he seems hesitant. When Garrett inquires as to why, Picard explains his concern that if they return back with future knowledge, it could upset the timeline even more than their current position has done. Garrett says that they barely escaped with their lives. Picard tells Garrett that history never recorded their last stand against the Romulans. Garrett says they responded to a distress call from Narendra III and engaged the Romulan forces attacking the outpost but that there were four Warbirds against the lone Enterprise. Picard tells her that the outpost was destroyed, and laments that if a Federation starship could have rescued a Klingon outpost, it just might have averted twenty years of war.

Back aboard the Enterprise-C, Castillo struggles with the news that he is twenty-two years out of time, as Lt. Yar works to bring the weapons systems up to spec, and attempts to rationalize the situation. Castillo wonders about his family and laments that they're probably dead but Tasha tells him that that's not necessarily true. She then tells Castillo that he might not like the future as the war has been very long. She tells him that the Federation has lost more than half the Starfleet to the Klingons. Castillo remarks that negotiations for a peace treaty were well underway when the Enterprise left on her mission. Tasha says there have been a lot of changes. Castillo suggests she fill him in on them.

Picard and Data confer

Back on the Enterprise-D, Data tells Picard that the anomaly is likely symmetrical. Picard asks Data about what would happen if Enterprise-C were to return through the rift. Data tells him that she would emerge in the midst of battle, at almost the exact instant she left. Picard asks if there's any chance of the ship surviving and Data says there isn't. Picard realizes then that sending the Enterprise-C back would be a death sentence.

Having returned to the Enterprise, Yar tells Castillo that it was the first Galaxy-class battleship built by the Federation and that Enterprise can transport as many as six thousand troops at once. Tasha says she was lucky to get the Enterprise and Castillo says he was too, referring of course, to the Enterprise-C. They arrive at sickbay and brief Captain Garrett on the Enterprise-C's current tactical state. When Garrett tells Castillo to concentrate on the ship's weapon systems, Yar tells her that there are Klingon battleships in the area. With that news, Garrett sits up, asks Castillo why she wasn't informed and then tells an intervening Beverly Crusher that she must resume her duties; when Crusher protests that Garrett needs another 24 hours of rest, Garrett tells Crusher that 24 hours might as well be 24 years.

Guinan once again comes to Picard in the conference lounge, now transformed into a strategic operations center. Picard asks if she has any more information, but Guinan doesn't. Without more information, without proof, Picard can't let them return. Guinan states he must. With barely restrained anger and slamming his fist on the table, Picard tells her the Enterprise-C crew would die moments after returning. Guinan tells Picard that she wishes she had more information but she doesn't. She only has a very strong feeling that this is wrong. Picard then asks who decides which timeline is the right one? Guinan says she does. That isn't good enough for Picard. He will not allow one hundred and twenty-five people to sacrifice their lives on her "feeling." Forty billion people have already been lost in this war, Guinan snaps back, a war that isn't and shouldn't be happening. She repeats that the only way to save those billions is to sacrifice that small group of people. But there is no guarantee of success, and everything Picard is tells him that the idea is wrong, dangerous and futile. Guinan tells Picard that in all the years he's known her, she's never forced herself on anyone, or to take a stand based on whimsical triviality. Guinan tells Picard that she's told him what he must do and Picard only has his trust in her to base his decision on.

Guinan then returns to Ten Forward, where she runs into Yar and Castillo, discussing improvements to the deflector system, how her Enterprise could now probably last twice as long in a firefight than the Enterprise-C. Guinan feels extreme uneasiness at Yar's very presence. There is a brief, awkward conversation between the two in regards to Yar ordering their food rations for the meal. Yar tells Castillo that is the first time she's ever seen Guinan like that. While Guinan goes to prepare their food, Yar and Castillo's conversation continues, with Castillo's head spinning a little due to the tactics that Tasha explained, which were more than what he learned at the Academy. Yar tells him he'll need it. Then the conversation heads toward more personal territory. Tasha asks what she should call him, now that they've decided they're probably past referring to each other by rank. Yar tells Castillo to call her Tasha and Castillo says everyone except his mother, who calls him Richard, calls him Castillo. But when Tasha tries calling him Castillo, he decides he'd rather her call him Richard. Just then, their conversation is interrupted by a call from Picard, ordering all senior officers to his ready room. Heading out, Yar and Guinan share another uncomfortable glance.

Picard briefs the senior officers on his decision. Crusher is astounded that Picard is going to send them back based solely on Guinan's intuition. Riker says there's no way the Enterprise-C can save Narendra III. Yar then tells Picard that Captain Garrett reported four Romulan Warbirds, leaving the Enterprise-C severely outmanned and outgunned. La Forge then presents the possibility of re-arming the Enterprise-C with modern weapons, but Picard vetoes it, saying if they do that they'll alter the past. Riker says isn't that what they're talking about but Picard says they're talking about restoring the past. La Forge wonders how Guinan would know history has been altered if she's been altered along with everyone else. Data suspects that possibly her species has a perception which goes beyond linear time.

Picard's senior officers are skeptical of his decision to return the Enterprise-C to the past.

Picard says there's much about her people they don't understand but fundamentally she is correct as a ship from the past has traveled through time and there is no way for them to know what effect that might have on the present and that they may never know but Picard has decided the consequences are too great to ignore. When Picard tries to dismiss them, Riker decides to speak again, although Picard tries to stop him, telling Riker that he's not seeking their consent and that this was merely a briefing. Riker though, with all due respect, tells Picard he's asking 125 people to die a meaningless death, but Data disagrees that it would absolutely be meaningless, pointing out that since the Klingons regard honor above all else, that if the crew of Enterprise-C died fighting for the survival of a Klingon outpost, it would be considered a meaningful act of honor by the Klingon Empire. Picard notes that their deaths might prevent the entire war, noting if Enterprise-C returns to the battle and its mission is a success, it will irrevocably change history, creating a new future for all of them. Having considered all the alternatives, Picard decides to go with Guinan's recommendation and this time, rather emphatically dismisses everyone.

Preoccupied by a comment made by La Forge and Crusher about whether they'll even be alive in an alternate timeline as they depart the ready room, Yar joins Data in the bridge's fore turbolift. Data makes a point when Yar comments that she's worried about what will happen to Castillo; Data tells her that if history is restored, they will have no memory of these events. This disturbs Yar even more.

As the crew of the Enterprise-C continue repairs, Garrett and Picard discuss possibilities for the ship either staying or returning, and the probability of Guinan's accuracy. Picard trusts her judgment. Garrett knows there is no chance for survival, and suggests the Enterprise-D return with them, and Picard says he can't. Garrett accepts that, saying Picard doesn't belong in her time any more than she belongs in Picard's. She then tells Picard how many of the Enterprise-C's crew want to return, some for not wanting to be without their loved ones and some because they don't like the idea of sneaking out in the middle of a fight. But Garrett has told her crew that the Federation needs another ship against the Klingons and they need to get used to the idea. Picard then tells her if she goes back it could be much more helpful. He then lowers his voice and reveals a disturbing fact to Garrett: the war is going very badly for the Federation, much worse than is generally known. According to Picard, Starfleet Command believes that defeat is inevitable and within six months, they may have no choice but to surrender. Garrett asks if this was caused by their presence. Picard says that one starship can make no impact in the present... but twenty-two years ago, one ship could stop the war before it starts.

Garrett tells Castillo to inform the crew they will return to their own time. She promises Picard that the Romulans will get a good fight, and that history will remember their actions. Picard tells Garrett he knows they will. As Picard beams back to the Enterprise-D, Yar and Castillo say their goodbyes but they are interrupted by an attack from a Klingon Bird-of-Prey, on a scouting mission. Yar mans the tactical station quickly and prepares to fight the Klingons. Garrett contacts the Enterprise-D and asks if Picard made it safely back and Riker acknowledges that he did. Despite fire from the Enterprise-D, the Bird-of-Prey scores some crucial hits on the Enterprise-C, causing a panel near Garrett to explode in sparks, sending her to the ground. As the Bird-of-Prey disappears under cloak, Picard hails Garrett and asks for a damage report but there is no response. After a second hail, Yar contacts Picard and reports that Captain Garrett is dead. Garrett has a piece of shrapnel imbedded in her head.

In the Strategic Operations Center, Castillo enters and tells Picard he is prepared to lead the Enterprise back himself. Riker though is skeptical as Castillo is the last surviving senior officer, having limited support from ops, no tactical, as well as reduced staff in engineering. Castillo interrupts Riker and tells Picard he has good people who wish to do their jobs. Riker believes history didn't mean for the Enterprise-C to enter this battle without Captain Garrett and while Castillo can't speak to that extent, he knows he can get the job done. Just then Data contacts Picard and informs him that likely due to the battle with the Klingons, the temporal rift is destabilizing. Tasha says they can't remain there as their coordinates have been transmitted to the Klingon Command. Castillo says then that he intends to return unless Picard orders him otherwise. He then tells Picard that he can have his ship ready in a few hours, that they only sustained moderate damage. With that information, Picard gives his assent and tells Castillo that they will provide cover.

A farewell kiss

Yar takes Castillo to the transporter room where they bid each other farewell again and then after joking about how they seem to have all the time one can afford to have, share a tender kiss, and then Castillo beams back to the Enterprise-C. From there, Yar goes to Ten Forward to confront Guinan about her fate in the other timeline. Guinan says she doesn't have alternate biographies of the crew, but Yar says there's something to the way Guinan looks at her recently and that they've known each other too long for these secrets. Guinan finally reveals that she feels like they weren't meant to know each other at all. Guinan then tells Yar that she's supposed to be dead and while she doesn't know how, she does know it was an empty death, that Yar was killed without reason or purpose.

Resolved, Yar meets Picard in his ready room and asks for a transfer to the Enterprise-C, which is in need of a tactical officer. Picard asks why and she says they need one, but Picard says they need her here. Yar then tells him she's not supposed to be there and that she's supposed to be dead. Picard allows Tasha to sit and is also disturbed that Guinan felt it necessary to give Yar that information, but Yar responds that she wanted to know. Picard tells Yar she doesn't belong on Enterprise-C. Tasha agrees, she says that Captain Garrett belongs there but she's dead. She then says there may be some logic in her request, which Picard angrily disagrees with, saying that, after he calms his voice, "There's no logic in this at all! Whether they succeed or not, the Enterprise-C will be destroyed." Yar says that with someone skilled at tactical they might be able to make the difference in the conflict. It may only be seconds or minutes, but that could be the time it takes to change history. Yar says she didn't like the thought of dying for no real reason and that, knowing the risks that come with being a Starfleet officer, if she is to die being one, she wants that death to count for something.

Picard considers for a moment, and then simply and quietly, grants Yar permission to go. She stands, thanks Picard, and leaves the Enterprise-D for the last time.

Aboard the Enterprise-C, Castillo is making final preparations for departure, placing crewmembers at ops and conn, just as Tasha reports for duty at tactical. Incredulous, Castillo wants to know what she's doing and she tells Castillo about how Captain Picard approved her transfer request. Castillo tells Yar they're going back through the rift, into battle and not coming back. Yar says that's why she came. Quietly, Castillo then tells her he doesn't want her aboard, but Yar dares him to find someone in his crew better suited than her to do the job. Castillo knows she is right and welcomes Yar aboard the Enterprise-C. Starting to step away from her, he orders her to take her station. Yar does so as Castillo moves over and sits in the captain's chair....

"Military log, supplemental. Lieutenant Tasha Yar has transferred to the Enterprise-C, where she has taken over tactical duties. Meanwhile, our long-range scanners have picked up Klingon battle cruisers on an intercept course."

Wesley reports three K'Vort-class battle cruisers are en route to intercept the two Enterprises. Picard notes how the Klingons don't even bother to cloak themselves. Riker is surprised at their audacity, after the pasting they apparently gave the Klingons during a recent battle at Archer IV.

Picard nods, and then addresses the crew:

"Attention all hands. As you know, we could outrun the Klingon vessels. But we must protect the Enterprise-C until she enters the temporal rift. And we must succeed! Let's make sure history never forgets... the name... Enterprise. Picard out." Listenfile info

The battle begins as the Klingon ships focus all of their firepower on the Enterprise-D, whose shields hold. Riker, manning the tactical station, reports photon torpedoes ready and Picard orders them fired using dispersal pattern Sierra. Data reports one enemy ship was hit with moderate shield damage. Another volley from the Klingons causes minor damage to the Enterprise's secondary hull. As Picard orders a course change, Wesley reports one of the enemy ships is breaking off to attack the Enterprise-C. Picard tells Wesley to keep them within 200 kilometers of Enterprise-C and Wesley turns course to intercept that Klingon ship, with Riker returning fire after the Klingons attack the Enterprise-C. La Forge reports from engineering that a starboard power coupling is down and antimatter containment fields suffers damage. The tactical situation for the Enterprise dims greatly as the Klingon warships flank the ship in an attempt to draw them away from the Enterprise-C. Picard then orders continuous fire of all phaser banks.

The Enterprise fires its forward phasers...

...with deadly results

As the Enterprise begins to fire continuous phaser blasts against the Klingons, a focused attack breaks through the shields of one of the ships, destroying it in seconds; but this is only a small victory, however, as the remaining ships knock out the main sensor array and cause critical damage to the warp core. The shields collapse, and the containment field is failing. As La Forge works to shut down the warp core, plasma coolant bursts free of the core manifold and the warp core builds to overload, with La Forge being unable to stop it; there are two minutes until a core breach.

Data reports on Picard's request that Enterprise-C is now fifty-two seconds from the rift, which is more than enough time.

The death of Will Riker

With his ship's destruction now inevitable, Picard orders all remaining power to defensive systems. Unfortunately, Data reports power couplings have been severed in the main phaser banks and he cannot bypass. The Enterprise is hit again and Riker is killed when part of the tactical console explodes. The Klingons signal, demanding that the Enterprise surrender to them.

"That will be the day.."

"That will be the day" Picard sneers and leaps the tactical rail, trying to fire the phasers himself. After several tries, the phasers fire on one of the Klingon ships, who respond by continuously firing on the Enterprise. Picard continues trying to fire as the bridge becomes engulfed in flames.

The Klingon ships batter away at the now-helpless Enterprise-D. As the ship is mere seconds away from being destroyed, the Enterprise-C makes it back through the rift.

The timeline is restored and Picard stands on the bridge in the exact spot he was before the timeline diverged. He asks for a report. Worf reports that his sensor readings fluctuated and what appeared to be a ship has now vanished. Data reports the anomaly is closing in on itself. Picard then orders a class 1 probe left behind to monitor the rift's final closure. He then orders Wesley to set course for Archer IV. Just then, Guinan calls up and asks if everything is all right. Picard and Riker are surprised to hear her on the intercom. He then tells Guinan everything is fine and asks if there's anything wrong. In Ten Forward, Guinan says no, that nothing's wrong and she's sorry to have bothered them. She then smiles, and goes to a table and sits opposite from La Forge and asks...

"Families. There should be children on this ship."
"What? Children on the Enterprise? Guinan, we're at war!"
"No we're not! At least we're not... supposed to be. This is not a ship of war. This is a ship of peace."

- Picard and Guinan in the alternate timeline, discussing about how changed seems to be the ship.

"Is there any possibility she could survive?"
"None, sir."
"Then sending them back... would be a death sentence."

- Picard and Data talking in the alternate timeline about the Enterprise-C's hopeless chance of defeating the Romulans

"Who is to say that this history is any less proper than the other?"
"I suppose I am."
"Not good enough, damn it! Not good enough! I will not ask them to die!"
"Forty billion people have already died! This war's not supposed to be happening! You've got to send those people back to correct this!"
"And what is to guarantee that if they go back they will succeed? Every instinct is telling me this is wrong, it is dangerous, it is futile!"
"We've known each other a long time. You have never known me to impose myself on anyone or take a stance based on trivial or whimsical perceptions. This timeline must not be allowed to continue. Now, I've told you what you must do. You have only your trust in me to help you decide to do it."

- Picard and Guinan in the alternate timeline

"The war is going very badly for the Federation, far worse than is generally known. Starfleet Command believes that defeat is inevitable. Within six months, we may have no choice but to surrender."
"Are you saying all this may be a result of our arrival here?"
"One more ship will make no difference in the here and now, but twenty-two years ago, one ship could have stopped this war before it started."

- Picard and Garrett in the alternate timeline

"But there's something more when you look at me, isn't there? I can see it in your eyes, Guinan. We've known each other too long."
"We weren't meant to know each other at all. At least, that's what I sense when I look at you. Tasha, you're not supposed to be here."

- Yar and Guinan in the alternate timeline

"Mr. Castillo?"
"Yes, Captain?"
"Inform the crew - we're going back!"

- Captain Rachel Garret to Castillo, after Picard reveals the assistance of the Enterprise-C at Narendra III could prevent the war

"[...] at least with someone at Tactical, they will have a chance to defend themselves well. It may be a matter of seconds or minutes, but those could be the minutes that change history. Guinan says I died a senseless death in the other time line. I didn't like the sound of that, Captain. I've always known the risks that come with a Starfleet uniform. If I'm to die in one, I'd like my death to count for something."

- Yar to Picard in the alternate timeline

"Attention all hands. As you know, we could outrun the Klingon vessels. But we must protect the Enterprise-C until she enters the temporal rift. And we must succeed! Let's make sure that history never forgets... the name... Enterprise. Picard out."

- Picard in the alternate timeline, before the final battle with the Klingon cruisers

"Federation ship Enterprise, surrender and prepare to be boarded."
"That will be the day."

- Klingon Captain and Picard in the alternate timeline, before the Enterprise-C enters the rift

The original idea for "Yesterday's Enterprise" was generated by Trent Christopher Ganino and submitted to Paramount on 15 April1989, as a spec script submitted through the open submissions policy introduced by Michael Piller in that year. (The Making of Yesterday's Enterprise, p. 18) This original version featured the appearance of an Enterprise from the past in the TNG time period, and Picard having to face the resultant dilemma of whether to return the ship and its crew to their indigenous time period. In this version, the ship did not cause any changes in the future. Picard was forced to decide whether or not to reveal the crew's fate before sending them back. At this point, the captain of the past Enterprise was Richard Garrett, whose last name derived from a pizzeria in Ganino's hometown, San Jose. (Star Trek: The Next Generation Companion, 3rd ed., p. 116; The Making of Yesterday's Enterprise, pp. 26-27)

At the same time, following a conversation with Denise Crosby at a convention, Eric Stillwell developed a story (along with Ganino) that would allow Tasha Yar to return to the series after a two-year absence. In this pitch, drawing from classic Star Trek episodes "The City on the Edge of Forever", "The Savage Curtain" and "Mirror, Mirror" – among others – a Vulcan science team would inadvertently cause the death of Surak, the founder of Vulcan philosophy, when a trip through the Guardian of Forever into Vulcan's ancient past goes wrong. As a result, the Vulcan people would never become the logical race that is known in the Star Trek universe. Instead, a Vulcan race more akin to the Romulan Star Empire would be engaged in war against the other powers of the galaxy, including the remnants of the Federation. As part of this alteration, Tasha Yar would be present amongst the crew of the Enterprise-D. Ultimately, Ambassador Sarek, who was on board the Enterprise to greet the returning science team, would sacrifice himself by returning to the past and taking the place of Surak, thus restoring the correct timeline. (The Making of Yesterday's Enterprise, pp. 23, 29-32) Stillwell commented, "We thought it would be really cool that someone from the future would replace someone in the past, and I always thought it was funny that their names were so similar anyway." (Star Trek: The Next Generation Companion, 3rd ed., p. 117) Although not used here, a similar theme went on to feature in the DS9 two-part episode "Past Tense, Part I" and "Past Tense, Part II", wherein Benjamin Sisko replaces historical figure Gabriel Bell.

When Stillwell pitched this idea to Michael Piller, Piller suggested combining it with Ganino's "Yesterday's Enterprise" story – which had also developed a Tasha Yar element by this point, largely on the suggestion of Piller, who had also wanted to find a way of bringing the character back – with Ganino and Stillwell retaining joint story credit. The Vulcans were replaced by the Klingons, and the Sarek/Surak plotline replaced with the idea that Yar would fill an absence on board Enterprise-C after the death of a female Captain Garrett. The finished storyline treatment was largely as broadcast, with the exception of Guinan's presence in the episode (in the completed pitch, an alien probe provided the crucial information about the timeline alteration). Some other minor plot points were lost between story and teleplay, including a Yar/Data subplot that was dropped, as Piller felt it was not the right arc for Yar's character. (The Making of Yesterday's Enterprise, pp. 34-46)

Production on the episode was originally scheduled for January 1990 following the Christmas hiatus; however, with the introduction of Guinan into the episode, the filming schedule needed to be moved up in order to accommodate both Crosby and Whoopi Goldberg. As a result, the pitched storyline needed to be turned into a teleplay over the Thanksgiving weekend of 1989, prior to filming commencing on December 11. Four members of the writing staff – Ira Steven Behr, Ronald D. Moore, Hans Beimler and Richard Manning – divided the episode amongst themselves in order to get it completed on time. In particular, Moore was responsible for the Yar-Castillo romance. Behr noted that although the writers were unhappy about the timescale pressure and having to work over a holiday, they enjoyed the chance to write an episode far darker than had been done in the past, with a great deal more tension – something many of the staff had felt was lacking in the series. Michael Piller added a final polish to the script, but agreed to be omitted from the credit to meet Writer's Guild rules which allowed only four names. ("Flashback: Yesterday's Enterprise", Star Trek Magazine issue 122; The Making of Yesterday's Enterprise, pp. 53-54, 65)

Ron Moore noted, "We brought Denise back to kill off Tasha Yar a second time. It was a great opportunity to send the character off in a big heroic sacrifice because nobody was really happy with the way she left the series in the first season. Nobody on the show really liked it, the fans didn't like it, I'm not sure even she really liked it. So 'Yesterday's Enterprise' was a chance to kill her right." (Chronicles from the Final Frontier, TNG Season 4 DVD special features)

Time and budgetary constraints put an end to the much more gruesome climactic battle sequence that was originally envisaged in the script. The only death to survive to the broadcast episode is Riker's – others that were written but unfilmed included the decapitation of Wesley Crusher and the electrocution of Data. (Star Trek: The Next Generation Companion 2nd ed., p. 117)

The transition effect seen as the timeline changed in the beginning of the episode was unscripted and only added in post-production. Originally, the change was accomplished merely by a cut, but it was felt that this was too confusing. However, due to the late nature of the change, the post-production staff neglected to add a corresponding transition effect as the timeline was reset at the end of the episode. (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 192)

This is the last episode of the series to feature all nine of its original regular cast members. Denise Crosby and Wil Wheaton would both appear in subsequent Star Trek episodes and films, but never the same ones.

This episode is the only on screen depiction of an encounter between two different Starships Enterprise.

The sets and atmosphere of the Enterprise-D were given significant alterations to reflect the more warlike nature of the starship:

The alternate bridge

The bridge was heavily redressed:

The mid-level, covering the command deck and the ramp access to Tactical, was raised up to the same level as the "horseshoe" console – access to Conn and Ops was by a series of steps directly in front of the command position.

The chairs at the command deck were removed, and replaced with a single command chair for Picard (to give his alter ego a sense of authority). As a result, Will Riker joined Tasha Yar at Tactical. The command deck would be raised again, albeit with all three command chairs intact (and not quite to the level of the horseshoe), for Star Trek Generations.

The equipment lockers at either side of the set were replaced with additional displays, with two freestanding consoles located at the forward edges of the raised mid-level. Two similar consoles (as well as side stations) were introduced for Generations as well.

A mesh grille was added to the underside of the tactical console.

The set's ambient lighting was significantly reduced; the overhead lighting changed from a bright white to a dull blue.

Ten Forward's back wall, usually adorned by a stylized sculpture, was replaced by a functional gray bulkhead, with the Enterprise registry details prominently displayed. Here, the ambient lighting was reversed from the change made to the bridge, being made significantly brighter.

Picard's ready room received similar lighting treatment to the bridge. In addition, the accoutrements that were normally present – the Enterprise painting, the couch, the works of Shakespeare, the NCC-7100 model, and Livingston – were all removed, and replaced with status displays and tactical maps.

The conference room set was cut in two to serve as two apparently different rooms – where Guinan confronts Picard for a second time, and where Castillo meets Picard, Riker, and Yar at the top of Act Four. Smaller versions of the conference room table were created, the Enterprise models removed, and a large tactical display added – in the first instance, at the "front" end of the set; in the second, along the back wall opposite the conference room windows.

Main Engineering was also significantly darkened for its brief appearance towards the end of the episode, the lighting dominated by the warp core.

The ambient noise aboard the ship was increased; consoles and displays were made much more audible, the usually unheard engines were made into a dull roar, intraship communications were general announcements, rather than direct hails person-to-person, and the door "swoosh" was made more audible and more reminiscent of the sound effect used in the original series.

In contrast to Captain's log and Stardates, the alternate timeline Picard records a Military log using "combat dates." However, an Okudagram on Picard's desk, seen shortly before Yar enters to ask for a transfer to the Enterprise-C, shows "Captain's log: Captain J-L Picard."

Red and yellow alert was not used, instead "Battle Alert" was used, followed by a "Condition" which was either yellow or red.

As opposed to the leisurely state of the Enterprise's corridors in the normal timeline, those in the alternate timeline are consistently crowded and full of jostling personnel, many running from place to place

The standard Starfleet uniform was also made more functional and military in design: the officers' uniform was changed to a band collar, instead of the the usual wishbone collar of the ordinary design, and a black "cuff" was added to the end of the sleeves. The junior officers' uniform was largely unchanged. All personnel wore a stylized Sam Browne belt, with the Starfleet delta at the clasp, designed to carry a type 2 phaser prominently on the left hip. The officers' version omitted the double strap across the right shoulder and around the left flank.

"Yesterday's Enterprise" of course marks the return of Denise Crosby as Tasha Yar to TNG, after Tasha's death in "Skin of Evil" (Crosby's last episode filmed was "Symbiosis", which aired before "Skin of Evil"). The events of the episode allowed her to return as Sela, in the "Redemption" and "Redemption II" episodes (as well as later in "Unification II").

Picard addresses Riker as "Commander" in the alternate timeline, instead of the usual "Number One", revealing Picard and Riker to be on less friendly terms with one another than in the main timeline. Ronald D. Moore remarked, "This was just another nuance we threw in to show the differences between "our" reality and the darker alternate reality." (AOL chat,1997) Elsewhere, Moore commented, "[I]t was a lot of fun to...see Picard biting Riker's head off." (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 192)

Tasha tells Castillo that she has been serving on the Enterprise for four years, implying that in the alternate universe the Enterprise-D has been in service longer than its counterpart by at least a year. She also tells him that the Enterprise was the first Galaxy-class warship.

When Tasha is telling Castillo the specifications of the Galaxy-class starships, the loudspeaker in the background is calling for a "Lieutenant Barrett". This is a reference to Majel Barrett, voice of the computer and the actress who portrayed Lwaxana Troi. (Star Trek: The Next Generation Companion 2nd ed., p. 117) Also, in the scene where Picard and Garrett meet in sickbay, a call for Dr. Selar can be heard.

The beginning of the episode, during the normal timeline, saw the introduction of Worf to prune juice, which would become his drink of choice.

This episode is one of only a very few where Guinan is seen on the bridge.

At the end of the episode when Geordi La Forge is talking to Guinan, La Forge is still in the alternate uniform.

Michael Piller remarked, "That was a classic episode. I never met Denise Crosby in person, but I am sure an admirer. She did a great job for us. That's just about as neat a show as we could do. It was as entertaining and unique a time travel show as you'll ever see. I don't know that there was a better episode third season. Hell, Picard sends 500 [sic] people back to their death on the word of the bartender. Come on, that's hard. I was very happy with it and, frankly, I give the credit to the director and the cast and the people who post-produced it. The script was not one of the best scripts we wrote that season. Conceptually, it was marvelous, coming out of the heads of some people here...There are little holes in the episode that we couldn't fix. It was such a complicated and fascinating premise, but it was ultimately the character material that really made everybody proud." (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 192)

This episode won an Emmy Award for Outstanding Sound Editing for a Series and was also nominated for Outstanding Sound Mixing for a Drama Series and Outstanding Achievement in Music Composition for a Series (Dramatic Underscore) (Dennis McCarthy).

The episode was voted the most popular episode of the series on six separate occasions – by Starlog readers in 1993 and by a viewer poll in 1994, and was voted as the most popular episode of all-time by UK Trek fans in 1996. The US publication TV Guide listed it as one of its top five all-time Trek classics in 1996 and again in 2002. Entertainment Weekly also ranked it as the #1 episode on their list of "The Top 10 Episodes" to celebrate the 20th anniversary of Star Trek: The Next Generation. [4]

In "Back to Back" the Klingons destroy the Enterprise-C before it enters the rift, the Enterprise-D flies away, but the war is lost and Federation becomes a member of the Klingon Empire. Picard is imprisoned before he organizes a rebellion with the help of the Borg, who eventually destroy the Klingons.

The novel Q-Squared establishes that in the military timeline from this episode, Deanna Troi's absence from the Enterprise was due to the Betazoids being wiped out by the Klingons. The novel also indicates that in this version of the military universe, when the Enterprise encountered the Enterprise-C, the entire crew had already perished- life support having failed and the crew dying over a day before the Enterprise-D arrived in the area-, and so Picard simply orders the ship's destruction.

The novel Engines of Destiny establishes that because Guinan left an echo of herself inside the Nexus, she has a perception into various timelines and universes giving an explanation as to how she knew the timeline had been altered in this episode and the repercussions of the events in this episode seen later in TNG: "Redemption II".

A very similar, if not almost identical, timeline appeared in the novel Q&A, in which the Enterprise-E had still been built, but where the Klingons had completely destroyed the Federation. Picard was the only known Human left after his entire crew had been killed, and he was chained to the bottom of his command chair as a sort of trophy of war for General Worf, the commander of this ship.

During the third anniversary of Star Trek Online, the fate of the Enterprise-C revealed that they were sent forward to the year 2409 instead of 2344. In this current timeline (same as the military), the war was lost for both Empire and Federation with the Tholian Assembly conquering them. The Enterprise's crew was brought to a mining facility as slave labors. With the player's help and a future timeship, they managed to break captivity and return to 2344.